JP6369715B2 - DC motor driving circuit, sheet feeding device, and image forming apparatus for driving bottom plate of sheet feeding device - Google Patents

Description

The present invention relates to a driving circuit for a DC motor for driving a bottom plate that drives a bottom plate that can be moved up and down by placing a sheet of a paper feeding device, a paper feeding device, and an image forming apparatus.

2. Description of the Related Art Conventionally, there is known a paper feeding device in which paper is stacked on a bottom plate that can be raised and lowered, and the bottom plate is raised according to the number of consumed paper to feed the paper at a constant top height. ing.

A DC motor is used as a drive source for the bottom plate, and a substrate on which a drive circuit for driving the DC motor is mounted is disposed in the sheet feeding device. The sheet feeding device has a cover that can be opened and closed, and is configured such that when the cover is opened, the bottom plate automatically descends and sheets can be replenished on the bottom plate.

In general, a polarity switching method using an H-bridge circuit (full-bridge circuit) is adopted for a DC motor drive circuit. That is, the forward rotation, reverse rotation, stop, and brake of the DC motor are selected according to the combination of on / off of the four switching elements of the H bridge circuit.

Even if a serious failure such as a failure of the switching element, a disconnection, a ground fault, a restraint state of the DC motor, or a short circuit of the winding of the DC motor occurs in the drive circuit of the DC motor, a serious failure such as smoke generation or burning does not occur. Some of them incorporate an abnormality detection circuit. As soon as an abnormality is detected, the abnormality detection circuit turns off the power supply relay to cut off the power supply to the H bridge circuit and the DC motor (see Patent Document 1: Japanese Patent Application Laid-Open No. 2009-278803). .

If a DC motor drive circuit malfunctions or a microchip that issues a command to the drive circuit malfunctions, the bottom plate that should be lowered suddenly rises with the cover of the paper feeder open to replenish paper May cause malfunction.

Accordingly, an object of the present invention is to make the bottom plate unable to rise when the cover of the paper feeding device is opened.

  In order to achieve the above object, the present invention provides a DC motor drive circuit for driving a bottom plate that can be moved up and down by placing paper in a paper feeding device, and the drive circuit is connected to a power input terminal of the DC motor. First switching means for switching the polarity of the power supply to be connected, power feeding means for feeding power to the drive circuit, current detection means for detecting current flowing in the drive circuit, and control for switching the first polarity switching means The control unit is configured to, based on a command from the sheet feeding device, the DC motor in a normal rotation mode for lowering the bottom plate, a reverse rotation mode for raising the bottom plate, and a stop mode for stopping the bottom plate. The mode is switched to four brake modes in which a brake is applied to the bottom plate, and the magnitude of the current flowing through the drive circuit is determined based on a detection value of the current detection means. When the current value is less than or equal to the current value, the power supply means is maintained in a power supply mode for supplying power to the drive circuit, and when the magnitude of the current flowing through the drive circuit exceeds the predetermined reference current value, the power supply means is supplied to the drive circuit. A control unit that switches to a non-power supply mode that does not supply power and an open / closed state of the cover of the paper feeding device that opens and closes for loading and unloading of the paper with respect to the paper feeding device are detected. There is provided a drive circuit for a DC motor for driving a bottom plate of a sheet feeding device, comprising: a second switching unit that switches a polarity of a power source connected to a power input terminal of the DC motor so that the switching is impossible.

The present invention detects the open / closed state of a cover of a paper feeding device that opens and closes for loading / unloading of paper with respect to the paper feeding device, and when the cover is in an open state, the DC motor cannot be switched to the reverse rotation mode. Since the 2nd switching means which switches the polarity of the power supply connected to a power supply input terminal was provided, the malfunctioning which the bottom plate of a greasing apparatus raises in a cover open state can be prevented reliably.

1 is a front view of a sheet feeding device using an H-bridge circuit of a DC motor of the present invention and an image forming apparatus equipped with the sheet feeding device. It is a see-through | perspective perspective view of the internal structure which abbreviate | omitted the drive mechanism of the paper feeder. FIG. 6 is a perspective view illustrating a driving mechanism of a paper feeding device. It is a block diagram of the drive circuit of the DC motor which concerns on embodiment of this invention. It is a figure which shows the action | operation of the drive circuit of the DC motor which concerns on embodiment of this invention. 3 is a flowchart for detecting an abnormality of a DC motor drive circuit according to an embodiment of the present invention. It is a block diagram of the drive circuit of the DC motor which concerns on the deformation | transformation embodiment of this invention.

Hereinafter, a driving circuit of a DC motor for driving a bottom plate of a sheet feeding device, a sheet feeding device, and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. In each drawing for explaining this embodiment, constituent elements such as members and components having the same function or shape are given the same reference numerals as much as possible to distinguish them, and then the explanation will be given. Is omitted.

FIG. 1 shows a sheet feeding device 10 as an embodiment of the present invention and an image forming apparatus 100 including the sheet feeding device 10. The sheet feeding device 10 has a rectangular casing 11 as shown in FIG.

A cover 12 is disposed on the front side of the housing 11. The cover 12 can be opened to the near side with a hinge portion (not shown) at the bottom as a center. The cover 12 is opened to replenish paper.

As shown in FIG. 2, a horizontal bottom plate 13 for stacking sheets and a DC motor 14 as a drive source for raising and lowering the bottom plate 13 in the vertical direction are disposed in the housing 11. A substrate 15 having an electric circuit for controlling the DC motor 14 is disposed on the inner surface of the housing 11.

In addition, an encoder sensor 16 and a lower limit sensor 17 are disposed above and below the housing 11. The encoder sensor 16 detects the rotation speed and rotation direction of the DC motor 14. The lower limit sensor 17 regulates the lower limit position of the bottom plate 13.

A switch 18 for detecting the open / closed state of the cover 12 is disposed in the housing 11. The switch 18 detects that the cover is closed by an operator (not shown) contacting the inner surface of the cover 12 with the cover 12 closed. When the cover 12 is open, as will be described later, one of the power input terminals of the DC motor 14 is connected to the ground, so that the reverse rotation of the DC motor 14, that is, the bottom plate cannot be raised.

As shown in FIG. 3, the rotation of the DC motor 14 is decelerated by a reduction unit 20 including a plurality of reduction gears, and is transmitted to the rotary shaft 21. A pulley 22 is fixed to both ends of the rotary shaft 21, and a toothed belt 24 is stretched between the pulley 22 and a pulley 23 fixedly disposed below the bottom plate 13. The left and right ends of the bottom plate 13 are fixed to the toothed belt 24.

The drive mechanism of the bottom plate 13 is configured as described above, and is configured such that the bottom plate 13 is lowered by rotating the DC motor 14 forward and the bottom plate 13 is raised in the direction of the arrow by rotating reversely.

(Embodiment of DC motor drive circuit)
FIG. 4 is a block diagram showing the drive circuit 30 of the DC motor 14 according to the present embodiment. The drive circuit 30 includes an H bridge circuit (full bridge circuit) 31 as a first switching means constituted by _four switching elements SE _{1 to} SE ₄ , a control unit 32, and a current detection circuit 33 as an abnormality detection circuit. And a voltage detection circuit 34 and a switch SW as second switching means. The switching elements SE _{1 to} SE ₄ are configured by field effect transistors (MOSFETs) or the like.

Two pairs of DC one of the two power input terminals OUT1, OUT2 of the motor 14 has four switching elements _{SE 1 ~SE 4 (SE 1,} SE 2), is connected to one (SE _3, SE _4), and The switch SW of the second switching means is disposed between the other of the power input terminals and the other of the pair of switching elements.

That is, between the first switching element SE ₁ and the second switching element SE ₂ of the H-bridge circuit 31 (drain side) and between the third switching element SE ₃ and the fourth switching element SE ₄ (drain side). The DC motor 14 and the switch SW are connected in series.

The power input terminal OUT1 on one side of the DC motor 14 is connected between the first switching element SE ₁ and the second switching element SE ₂ (drain side). The power input terminal OUT2 on the opposite side of the DC motor 14 is connected to the terminal COM of the switch SW.

The terminal NO of the switch SW is connected between the third switching element SE ₃ and the fourth switching element SE ₄ (drain side), and the terminal NC of the switch SW is connected to the ground. Then, by switching the switch SW to the terminal NO or terminal NC, between the power supply input terminal OUT2 of the DC motor 14 and the third switching element SE ₃ and the fourth switching element SE ₄ (drain side), or it is connected to ground I am doing so.

The switch SW can be configured integrally with the switch 18 described above, but may be configured separately using a relay or the like.

Between the first switching element SE ₁ and the third switching element SE ₃ of the H bridge circuit 31 (source side), a 24 volt power source is connected via the relay 35. Further, the second switching element SE ₂ and the fourth switching element SE ₄ (source side) are connected to the ground via the current detection resistor 36.

The voltage generated in the current detection resistor 36 is input to the current detection circuit 33. The current detection circuit 33 calculates the current value Ir flowing through the current detection resistor 36 from the voltage, compares the current value with the reference current value Is, and determines whether the current flowing through the DC motor 14 exceeds the reference current value Is. It is configured to detect whether or not. The reference current value Is may be configured to be changeable depending on the size of the load and environmental conditions (temperature).

The control unit 32 has two signal input terminals IN1 and IN2, and a signal having a 1-bit value is supplied to the two signal input terminals IN1 and IN2 from a microchip (not shown) mounted on the sheet feeding device 10. It has become. The four switching elements SE _{1 to} SE ₄ are switched on or off by a 1-bit value signal input to the signal input terminals IN1 and IN2 of the control unit 32 as shown in FIG. By the switching, each mode of stop, forward rotation, reverse rotation, and brake of the DC motor 14 is executed.

When the DC motor 14 rotates forward, the bottom plate 13 descends. At this time, the first switching element SE ₁ and the fourth switching element SE ₄ are on, and the second switching element SE ₂ and the third switching element SE ₃ are off. Therefore, the current flows in the order of the first switching element SE ₁ → the DC motor 14 → the switch SW → the fourth switching element SE ₄ → the current detection resistor 36 → the ground.

When the DC motor 14 rotates in the reverse direction, the bottom plate 13 rises. At this time, the first switching element SE ₁ and the fourth switching element SE ₄ are off, and the second switching element SE ₂ and the third switching element SE ₃ are on. Accordingly, the current flows in the order of the third switching element SE ₃ → switch SW → DC motor 14 → second switching element SE ₂ → current detection resistor 36 → ground.

The voltage detection circuit 34 is configured to detect a voltage generated between at least one source / drain of a switching element through which a current flows when the cover 12 is open. Here, the voltage generated between the source and the drain of the first switching element SE ₁ is detected. The voltages at the circled numbers 1 to 3 of the H bridge circuit 31 and the current detection resistor 36 are respectively input to the circled numbers 1 to 3 of the operational amplifier (op amp) of the voltage detection circuit 34. . In addition to the first switching element SE ₁ , a voltage generated between the source and drain of the third switching element SE ₃ may be detected. This makes it possible to detect a ground fault / rare short when the bottom plate is raised.

In this embodiment, the power input terminal OUT2 of the DC motor 14 is connected to the ground through the NC terminal of the switch SW when the cover is opened in order to prevent the bottom plate 13 from being raised when the cover 12 is open. ing. In this state, the current flows from the first switching element SE ₁ → the power input terminal OUT1 of the DC motor 14 → the power input terminal OUT2 → the NC terminal of the switch SW → the ground, and the DC motor 14 rotates forward (bottom plate lowering).

DC motor 14 when the cover is opened in order to the bottom plate 13 rotates in the reverse direction increases, the power input terminal OUT2 of the DC motor 14 must be connected to the third switching element SE _3. In this embodiment, since the power input terminal OUT2 is connected to the ground when the cover is opened, the bottom plate 13 cannot rise when the cover is opened. If the first switching element SE ₁ is turned off due to malfunction or failure when the cover is opened, there is no problem because the DC motor 14 stops without being energized.

Note that at the moment when the DC motor starts to move, a starting current larger than the current during the rotation of the DC motor flows. The magnitude of this starting current varies depending on the size of the load and environmental conditions (temperature).

Even if there is no abnormality in the drive circuit, when the starting current becomes larger than a predetermined reference current value, the current detection circuit 33 as the abnormality detection circuit of the DC motor 14 described above is erroneously detected as an excessive current, and the relay 35 detects the DC. The power supply to the motor 14 may be interrupted. If it does so, unless the drive circuit is reset, raising / lowering of the baseplate 13 becomes impossible, and although it is temporary, paper feeding operation | movement and paper supply cannot be performed.

Therefore, in this embodiment, as will be described below, the bottom plate 13 is reliably in the state in which the cover 12 is opened regardless of variations in the magnitude of the starting current of the DC motor 14 or malfunction of the drive circuit, microchip, or the like. A descent operation is started so that the subsequent paper supply can be performed smoothly.

FIG. 6 is an abnormality detection flowchart of the drive circuit of the DC motor according to this embodiment. When the power is turned on, detection of abnormal current of the DC motor 14 starts. First, in step S1, it is determined whether or not the cover 12 is open. If it is determined that the cover is open, the process proceeds to the next step S2. In step S2, the power input terminal OUT2 of the DC motor 14 is connected to the ground by switching the switch SW.

Following step S2, the DC motor 14 is started in step S3. When the DC motor 14 is activated, the relay 35 is turned on and the power source is connected to the H-bridge circuit 31. At this time, the switching element is in the switching state shown in FIG. In step S4, it is determined whether or not the starting current value exceeds the reference current value. In addition, you may comprise the said reference electric current value so that a change is possible with the magnitude | size of load, and environmental conditions (temperature).

The starting current is a current that flows at the moment when the DC motor 14 starts to move, and a larger current flows through the DC motor 14 than the current during the rotating operation. If the starting current value exceeds the reference current value, the power supply to the DC motor 14 is temporarily interrupted by the relay 35 in the next step S5. The time from the activation of the DC motor 14 to the power supply interruption is much shorter than the time until the bottom plate 13 starts to descend. Accordingly, the bottom plate 13 remains substantially stopped at a constant height.

The starting current value is detected not by the current detection circuit 33 but by the voltage detection circuit 34. This is because when the cover 12 is opened, the switch SW is switched to the ground-side terminal NC, no current flows through the current detection resistor 36, and the current detection circuit 33 does not work.

Next, in step S6, it is determined whether or not the power supply cutoff state has passed for a predetermined T seconds. T seconds is a very short time, for example, several milliseconds. If it is determined that T seconds have elapsed, power supply is resumed in step S7. In step S4, the magnitude relationship between the starting current value and the reference current value is determined again.

As long as the starting current value exceeds the reference current value, step S4 and step S5 are repeated many times. When it is determined in step S4 that the starting current value is equal to or less than the reference current value, continuous power feeding to the DC motor 14 is executed in step S8, and the lowering operation of the bottom plate 13 is started in step S9. When the lower limit sensor 17 detects the bottom plate 13, the DC motor 14 stops.

If it is determined in the first step S4 that the starting current value does not exceed the reference current value, no false detection will occur. In this case, continuous power feeding to the DC motor 14 is immediately performed in step S8.

Specifically, the continuous power supply is performed by switching the switching element as shown in (2) of FIG. Thereby, the descent operation of the bottom plate 13 is started by the forward rotation of the DC motor 14 in step S7.

Continuous power feeding is started after repeating S4 to S7 until the starting current value falls below the reference current value. As a result, it is possible to prevent the DC motor 14 from being inoperable (the bottom plate 13 cannot be lowered) due to the relay 35 being forcibly cut off due to erroneous detection of an excessive start-up current as in the prior art.

As a result, the time during which the starting current value exceeds the reference current value depends on the usage conditions (supply voltage of DC motor 14, winding resistance, winding inductance, deviation between brush center and magnet center angle, center of commutator slit, Even when it changes according to the deviation of the core slit center angle) and the environment (temperature), the bottom plate lowering operation corresponding to the changing time is possible.

(Modified embodiment)
FIG. 7 is a control circuit block diagram of the DC motor 14 according to a modified embodiment of the present invention. In this block diagram, unlike FIG. 1, the switch SW is connected to the signal input terminal IN <b> 2 of the control unit 32. The signal input terminal IN1 is directly connected to the microchip. Others are the same as in FIG. Depending on the operation contents of FIG. 5, the switch SW can be connected not to the signal input terminal IN2 of the control unit 32 but to the opposite signal input terminal IN1. In this case, the signal input terminal IN2 is directly connected to the microchip.

When the cover 12 is opened, the switch 18 is turned on, and the signal input terminal IN2 is connected to the ground-side terminal NC of the switch SW in order to disable the ascending operation of the bottom plate 13 when the switch 18 is turned on. Further, when the switch 18 is turned on, a signal is input from a microchip (not shown) to the signal input terminals IN1 and IN2 as shown in (2) of FIG.

In the cover open state, IN2 is connected to the ground and is always "0". For this reason, even if a signal for raising the bottom plate is input from the microchip due to a malfunction or the like as shown in FIG. 5 (3) with the cover open, IN1 is “0” as shown in FIG. Since IN2 becomes “0”, the bottom plate 13 is in the stop state.

Therefore, the bottom plate 13 cannot rise when the cover is open. Of course, when a normal bottom plate lowering signal is input from the microchip as shown in FIG. 5 (2), IN1 is “1” and IN2 is “0”, so the bottom plate 13 is normally lowered. .

Also in the modified embodiment of FIG. 7, the current detection circuit 33 and the voltage detection circuit 34 operate in the same manner as described above with reference to FIGS.

  As mentioned above, although embodiment of this invention was described, this invention can be variously deformed without being limited to the said embodiment. For example, in the above-described embodiment, the H bridge circuit 31 composed of a field effect transistor (MOSFET) or the like is used as the first switching means. However, the first switching means is not limited to the H bridge circuit 31 and any switching means is used. Can do.

Further, the bottom plate lowering due to the forward rotation of the DC motor 14 and the bottom plate rising due to the reverse rotation can be reversed by the drive mechanism of the bottom plate 13. In short, in the present specification, the “forward rotation” of the DC motor 14 refers to the rotation direction in which the bottom plate 13 is lowered, and the “reverse rotation” refers to the rotation direction in which the bottom plate 13 is raised.

DESCRIPTION OF SYMBOLS 10 Paper feeder 11 Housing | casing 12 Cover 13 Bottom plate 14 DC motor 15 Board | substrate 16 Upper limit sensor 17 Lower limit sensor 18 Switch 20 Deceleration unit 21 Rotating shaft 22 Pulley 23 Pulley 24 Belt 30 Drive circuit 31 H bridge circuit (1st switching means)
32 control unit 33 current detection circuit 34 voltage detection circuit 35 relay 36 current detection resistor 100 image forming apparatus SE ₁ -SE ₄ switching element SW switch (second switching means)

JP 2009-278803 A

Claims (5)

A driving circuit of a DC motor for driving a bottom plate that can be moved up and down by placing paper in a paper feeding device,
First switching means for switching the polarity of the power source connected to the power input terminal of the DC motor;
Power supply means for supplying power to the drive circuit;
Current detection means for detecting a current flowing in the drive circuit;
A control unit for switching the first switching unit, the control unit based on a command from the paper feeding device, the DC motor, the normal rotation mode for lowering the bottom plate, the reverse to raise the bottom plate There are four modes: a rotation mode, a stop mode for stopping the bottom plate, and a brake mode for applying a brake to the bottom plate, and the magnitude of the current flowing through the drive circuit is determined based on the detection value of the current detection means. When the current is less than a predetermined reference current value, the power supply means is maintained in a power supply mode for supplying power to the drive circuit, and when the magnitude of the current flowing through the drive circuit exceeds the predetermined reference current value, the power supply means is A control unit that switches to a non-feed mode that does not feed power to the drive circuit;
An open / close state of the cover of the paper feeding device that opens and closes for loading and unloading of the paper with respect to the paper feeding device is detected, and when the cover is in an open state, the DC motor power Second switching means for switching the polarity of the power source connected to the input terminal ,
The first switching means is composed of an H bridge circuit having four switching elements, one of the two power input terminals of the DC motor is connected to one of the two pairs of the switching elements, and the power input terminal The second switching means is disposed between the other of the pair of switching elements and the other of the pair of switching elements, and the second switching means connects the other of the power input terminals to the ground when the cover is open, When the cover is in a closed state, the other of the power input terminals is connected to the other of the pair of switching elements, and
A voltage detection circuit configured to detect whether a voltage between at least one drain and source of the switching element that is turned on when the cover is open exceeds a predetermined reference voltage value; and the control unit includes: In the open state, instead of the detection result of the current detection means, it is determined whether the magnitude of the starting current of the DC motor is within a predetermined reference current value based on the detection result of the voltage detection circuit, A driving circuit for a DC motor for driving a bottom plate of a sheet feeding device, wherein a power feeding unit is set to the power feeding mode or the non-power feeding mode . 2. The drive circuit for a DC motor for driving a bottom plate according to claim 1 , wherein a magnitude of a reference current value of the current detection means or the voltage detection circuit is made variable. A driving circuit of a DC motor for driving a bottom plate that can be moved up and down by placing paper in a paper feeding device,
First switching means for switching the polarity of the power source connected to the power input terminal of the DC motor;
Power supply means for supplying power to the drive circuit;
Current detection means for detecting a current flowing in the drive circuit;
A control unit for switching the first switching unit, the control unit having two input terminals to which a command from the paper feeding device is input, and a 1-bit value input to the two input terminals The DC motor is switched to four modes: a forward rotation mode for lowering the bottom plate, a reverse rotation mode for raising the bottom plate, a stop mode for stopping the bottom plate, and a brake mode for applying a brake to the bottom plate. And, based on the detection value of the current detection means, when the magnitude of the current flowing through the drive circuit is below a predetermined reference current value, the power supply means is maintained in a power supply mode for supplying power to the drive circuit, and A control unit that sets the power feeding means to a non-power feeding mode in which power is not fed to the driving circuit when the magnitude of the current flowing through the driving circuit exceeds the predetermined reference current value;
An open / close state of the cover of the paper feeding device connected to one of the two input terminals and opened / closed for loading / unloading of the paper to / from the paper feeding device is detected, and when the cover is open, the reverse rotation mode is set. Second switching means for giving a predetermined 1-bit value to one of the input terminals so that switching is impossible ,
The first switching means is composed of an H-bridge circuit having four switching elements, one of the two power input terminals of the DC motor is connected to one of the two pairs of the switching elements, and the power input terminal Is connected to the other of the pair of switching elements,
A voltage detection circuit configured to detect whether a voltage between at least one drain and source of the switching element that is turned on when the cover is open exceeds a predetermined reference voltage value; and the control unit includes: In the open state, instead of the detection result of the current detection means, it is determined whether the magnitude of the starting current of the DC motor is within a predetermined reference current value based on the detection result of the voltage detection circuit, A driving circuit for a DC motor for driving a bottom plate of a sheet feeding device, wherein a power feeding unit is set to the power feeding mode or the non-power feeding mode . A sheet feeding device comprising the driving circuit for the DC motor for driving the bottom plate according to any one of claims 1 to 3 . An image forming apparatus comprising the paper feeding device according to claim 4 .